Circular saw blades exhibit three types of vibration: a resonant vibration at a particular frequency usually during idling known as the "screaming" blade; a resonant response at many frequencies during cutting; and a forced vibration as opposed to resonant vibration which occurs at the tooth passage frequency and multiples of that frequency. A key to solving the first two problems is to increase damping but the solution is not usually adequate for the third vibration, since forced vibration is not as sensitive to damping as are free resonant vibrations.
The vibration response of circular saw blades may involve both diametrical and circumferential travelling waves. This modal response is usually excited near the periphery by aerodynamic disturbances or the actual cutting process. It is known that contributions to the radiated sound are greatest for circumferential travelling waves near the periphery where vibrational amplitudes are large and the structural wave length is large compared to the acoustic wave length. Noise sources in the vicinity of the cutting tool are usually aerodynamic or blade vibration in nature and the reduction of sound radiation through the use of shields, partial or total enclosures, have been utilized. Other approaches have been made to reduce tool sound radiation for circular saws which involve alteration of the saw blade itself by increasing the blade damping. The disclosure in U.S. Pat. No. 3,107,706 presents inclined slots which are circumferentially spaced about the periphery of the saw blade with inserts installed in the slots in the form of slugs in spaced relation to the saw periphery. Other disclosures for modifying vibration are set forth in U.S. Pat. Nos. 3,563,286; 3,812,755; and 4,034,638. In addition, inclined slots that do not extend to the periphery of the blade with collars that do not extend to the slots have been introduced by Industrial Carbide Saw and Tool Corp. of Louisville, Kentucky, and is the subject of a publication entitled: Noise Reduction Achieved With Slotted Blades by Michael S. Bobeczko and B. B. Henry which discloses the saw blade of Industrial Carbide Saw and Tool Corp.
It can be shown that reduction of saw blade vibration response can be achieved through increased damping (see Appendix A). This may be achieved in a number of ways such as by interrupting wave propagation due to circumferentially travelling waves and by providing an appropriately designed energy-absorbing termination in the form of a collar which may dissipate the propagated energy and by radial slots in the circular saw blade that are circumferentially spaced. The blade segments may, if desirable, be stiffened by ribs in the radial slots that will transmit little vibrational energy.
Wave motion is effectively impeded in the circumferential direction by the radial slot. The stiffening ribs, if utilized, are preferably of a design that will be capable of transmitting little vibrational energy due to the large change in cross-sectional area and/or material properties. The stored vibrational energy in each section of the saw blade will take the path of least resistance which would result in energy flow inward into the damping collars where dissipation occurs due to shear stresses in the damping layer. The damping collars are not rigid with respect to high frequency vibration and provide a sink for energy dissipation rather than a reflective termination. By reducing the tendency for circumferential waves to form around the blade, the waves do not reinforce but terminate within a closed system.
It is, therefore, an objective of this invention to provide a circular saw blade with means for altering wave propagation and to absorb the vibrational energy in damping means centrally located where dissipation may occur due to shear stresses.
Another objective of this invention is to provide a circular saw blade with radially-extending slots which may have means in the slots for increased structural integrity to the formed blade segments and a damping member that is centrally located for receiving vibrational energy.
Other objectives and many of the attendant advantages of this invention will become more readily apparent to those skilled in the art of noise control and vibration in tools from the following detailed description of the invention and the claims in which equivalents are contemplated.